Archie was an idiot. Jughead could not even begin to comprehend how anyone could turn his head when he had Betty wrapped around his finger. He acknowledged that Veronica was attractive, but she was no Betty Cooper. Jughead was almost angry at Archie for turning her down.
There has never been a single girl who made Jughead feel the way he did when he thought about Betty. The only females he had ever even wanted in his life were his mother and sister, affectionally know as Jellybean, but obviously he felt very differently about them than he did Betty. She was the only girl who he ever truly cared for, whom he wanted to be happy. That's why he wanted to slug Archie in the face.
It wasn't even just that Archie had hurt her, it was that Archie was an idiot. He must be stupid if he even for a moment thought there was anyone out there more desirable than Betty. Jughead had already made up his mind about Veronica and he was not a fan. She was entitled and catty, and he knew that she too was involved in Betty's heartbreak. Hearing about their kiss at school, the only topic of conversation floating around the halls it seemed, made him ill. He and Archie weren't exactly buddy-buddy anymore, but he still had faith in the guy. But now? Jughead was too angry to be rational.